珠江口羽流锋浮游植物群落对大气沉降的生态响应

Response of phytoplankton community to atmospheric deposition along Pearl River plume front

受季风强迫,珠江淡水羽在南海北部广泛形成羽流锋面,而浮游植物群落通常在羽流锋面具有较高的生物量。南海北部毗邻珠江三角洲,陆源输入的大气沉降对该海区生态系统影响显著。利用2019年3月珠江口西部的现场调查数据,结合羽流锋面浮游植物群落分布的空间差异与大气沉降影响下的浮游植物群落生态学,分析两者对南海北部陆架区浮游植物粒径群落以及微微型浮游植物的耦合影响。研究表明,羽流锋面滨侧以小型(Micro)浮游植物群落为主,锋面海侧以微微型(Pico)浮游植物群落为主,而锋面区浮游植物群落粒径分布较为均匀,且生物量高。锋面区域环境因子差异导致浮游植物群落分布呈现较大的空间差异。在锋面区域,浮游植物群落生长总体受氮限制,而聚球藻的生长则受磷限制。锋面区域浮游植物群落内部种群对营养盐的需求和响应有所差异。大气干、湿沉降的添加均能够促进不同粒径浮游植物群落的生长:在锋面滨侧和锋面海侧,小型浮游植物群落在添加气溶胶颗粒或雨水后比微型(Nano)和微微型浮游植物群落表现出更大的竞争优势,生长率最高;而锋面区域浮游植物群落表现出更强的适应性,小型、微型、微微型浮游植物群落的生长速率均增加且无显著差异。大气沉降颗粒的添加显著促进了锋面系统微微型真核浮游植物与锋面滨侧聚球藻的生长,在锋面区域以及锋面海侧则抑制了聚球藻和原绿球藻的生长。

The Pearl River plume water can form an active plume front along the coastal northern South China Sea. A higher biomass of phytoplankton could exist along the plume front affected by hydrological factors. Atmospheric deposition from land-source input has a significant impact on the ecosystem of the Pearl River Delta zone. A field survey at the western part of the Pearl River Estuary was conducted in March 2019. Substantial variations of size-fractionation phytoplankton community and picoplankton were determined along a section, which affected by the plume front. Meanwhile, atmospheric deposition amendment experiments of three stations, covering different regions of the plume front, were conducted. Results showed that the size-fractionation phytoplankton community was dominated by microphytoplankton at the shore side of the front,picophytoplankton at the sea side of the front, and evenly distributed at the frontal zone with relatively higher biomass. At the frontal zone, the total phytoplankton community was limited by Nitrogen, while the Synechococcus showed a Phosphorus-limitation. Species among the frontal zone could show different nutrients demands. Atmospheric dry or wet deposition could stimulate the growth of three size-fractionation phytoplankton community. The microphytoplankton showed higher growth rate with atmospheric dry or wet amendments at shore side or sea side of the front, while the growth of three size-fractionation phytoplankton community could be stimulated indistinguishably. The addition of atmospheric deposition significantly stimulated the growth of Picoeukaryotes in the frontal system and of Synechococcus at the shore side of the front. Inhibited effects on Synechococcus and Prochlorococcus were found at the frontal zone and sea side of the front.